Scheduling request procedure for d2d communication

ABSTRACT

The present invention relates to a D2D capable a communication method and to a transmitting user equipment, which transmits data to a receiving user equipment over a direct link data channel, uses the services of the eNodeB in order to have resources allocated for transmitting said data. To this end the UE sends to the eNB scheduling information using resources of a subframe dedicated for standard uplink communication through the eNodeB, rather than using resources on the subframe dedicated to D2D data transmission. In order to allow the eNB to distinguish whether the received scheduling request is for allocating resources for transmitting data over the direct link channel or over the eNB, UE may send along with the scheduling information also identification information associated to the scheduling information.

FIELD OF THE INVENTION

The invention relates to a system and method for performing a schedulingrequest procedure in a device-to-device communication system. Theinvention is also providing the user equipment for performing themethods described herein.

TECHNICAL BACKGROUND Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving aradio-access technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. The detailed system requirements are given in 3GPP, TR 25.913(“Requirements for Evolved UTRA and Evolved UTRAN”, www.3gpp.org). InLTE, scalable multiple transmission bandwidths are specified such as1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieve flexiblesystem deployment using a given spectrum. In the downlink, OrthogonalFrequency Division Multiplexing (OFDM) based radio access was adoptedbecause of its inherent immunity to multipath interference (MPI) due toa low symbol rate, the use of a cyclic prefix (CP), and its affinity todifferent transmission bandwidth arrangements. Single-carrier frequencydivision multiple access (SC-FDMA) based radio access was adopted in theuplink, since provisioning of wide area coverage was prioritized overimprovement in the peak data rate considering the restrictedtransmission power of the user equipment (UE). Many key packet radioaccess techniques are employed including multiple-input multiple-output(MIMO) channel transmission techniques, and a highly efficient controlsignaling structure is achieved in Rel. 8 LTE.

E-UTRAN Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2. TheE-UTRAN consists of one or more eNodeBs, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe UE. The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control(MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP)layers that include the functionality of user-plane header-compressionand encryption. It also offers Radio Resource Control (RRC)functionality corresponding to the control plane. It performs manyfunctions including radio resource management, admission control,scheduling, enforcement of negotiated uplink Quality of Service (ULQoS), cell information broadcast, ciphering/deciphering of user andcontrol plane data, and compression/decompression of downlink/uplinkuser plane packet headers. The eNodeBs are interconnected with eachother by means of the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (S-GW) bymeans of the S1-U. The S1 interface supports a many-to-many relationbetween MMEs/Serving Gateways and eNodeBs. The SGW routes and forwardsuser data packets, while also acting as the mobility anchor for the userplane during inter-eNB handovers and as the anchor for mobility betweenLTE and other 3GPP technologies (terminating S4 interface and relayingthe traffic between 2G/3G systems and PDN GW). For idle state UEs, theS-GW terminates the downlink data path and triggers paging when downlinkdata arrives for the user equipment. It manages and stores userequipment contexts, e.g., parameters of the IP bearer service, networkinternal routing information. It also performs replication of the usertraffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theS-GW for a user equipment at the initial attach and at time of intra-LTEhandover involving Core Network (CN) node relocation. It is responsiblefor authenticating the user (by interacting with the HSS). TheNon-Access Stratum (NAS) signaling terminates at the MME and it is alsoresponsible for generation and allocation of temporary identities touser equipment. It checks the authorization of the UE to camp on theservice provider's Public Land Mobile Network (PLMN) and enforces userequipment roaming restrictions. The MME is the termination point in thenetwork for ciphering/integrity protection for NAS signaling and handlesthe security key management. Lawful interception of signaling is alsosupported by the MME. The MME also provides the control plane functionfor mobility between LTE and 2G/3G access networks with the S3 interfaceterminating at the MME from the SGSN. The MME also terminates the S6ainterface towards the home HSS for roaming user equipment.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called sub-frames. In 3GPP LTE eachsub-frame is divided into two downlink slots as shown in FIG. 3, whereinthe first downlink slot comprises the control channel region (PDCCHregion) within the first OFDM symbols. Each sub-frame consists of agiven number of OFDM symbols in the time domain (12 or 14 OFDM symbolsin 3GPP LTE (Release 8)), wherein each of OFDM symbol spans over theentire bandwidth of the component carrier. The OFDM symbols thus eachconsist of a number of modulation symbols transmitted on respectiveN_(RB) ^(DL)×N_(sc) ^(RB) subcarriers as also shown in FIG. 4.

Assuming a multi-carrier communication system, e.g., employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block is defined as N_(symb) ^(DL) consecutive OFDMsymbols in the time domain and N_(sc) ^(DL) consecutive subcarriers inthe frequency domain as exemplified in FIG. 4. In 3GPP LTE (Release 8),a physical resource block thus consists of N_(symb) ^(DL)×N_(sc) ^(RB)resource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (for further details on the downlinkresource grid, see for example 3GPP TS 36.211, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, version 8.9.0 or 9.0.0, section 6.2, available athttp://www.3gpp.org and incorporated herein by reference).

The term “component carrier” refers to a combination of several resourceblocks. In future releases of LTE, the term “component carrier” is nolonger used; instead, the terminology is changed to “cell”, which refersto a combination of downlink and optionally uplink resources. Thelinking between the carrier frequency of the downlink resources and thecarrier frequency of the uplink resources is indicated in the systeminformation transmitted on the downlink resources.

Further Advancements for LTE (LTE-A)

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the StudyItem description on “Further Advancements for E-UTRA (LTE-Advanced)” wasapproved in the 3GPP. The study item covers technology components to beconsidered for the evolution of E-UTRA, e.g., to fulfill therequirements on IMT-Advanced. Two major technology components which arecurrently under consideration for LTE-A are described in the following.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers (CCs) areaggregated in order to support wider transmission bandwidths up to 100MHz. Several cells in the LTE system are aggregated into one widerchannel in the LTE-Advanced system which is wide enough for 100 MHz,even though these cells in LTE are in different frequency bands. A UEmay simultaneously receive or transmit on one or multiple CCs dependingon its capabilities:

-   -   A Rel-10 UE with reception and/or transmission capabilities for        CA can simultaneously receive and/or transmit on multiple CCs        corresponding to multiple serving cells;    -   A Rel-8/9 UE can receive on a single CC and transmit on a single        CC corresponding to one serving cell only.

Carrier aggregation (CA) is supported for both contiguous andnon-contiguous CCs with each CC limited to a maximum of 110 ResourceBlocks in the frequency domain using the Rel-8/9 numerology.

It is possible to configure a UE to aggregate a different number of CCsoriginating from the same eNB and of possibly different bandwidths inthe UL and the DL.

It is possible to configure a 3GPP LTE-A (Release 10) compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may not be possible to configure amobile terminal with more uplink component carriers than downlinkcomponent carriers.

In a typical TDD deployment, the number of component carriers and thebandwidth of each component carrier in uplink and downlink is the same.Component carriers originating from the same eNodeB need not to providethe same coverage.

Component carriers shall be LTE Rel-8/9 compatible. Nevertheless,existing mechanisms (e.g., barring) may be used to avoid Rel-8/9 UEs tocamp on a component carrier.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time preserve orthogonality of the subcarriers with15 kHz spacing. Depending on the aggregation scenario, the n×300 kHzspacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

The Layer 2 structure with activated carrier aggregation is shown inFIG. 5 and FIG. 6 for the downlink and uplink respectively. Thetransport channels are described between MAC and Layer 1, the logicalchannels are described between MAC and RLC.

When carrier aggregation (CA) is configured, the UE only has one RRCconnection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides theNAS mobility information (e.g., TAI), and at RRC connectionre-establishment/handover, one serving cell provides the security input.This cell is referred to as the Primary Cell (PCell). In the downlink,the carrier corresponding to the PCell is the Downlink Primary ComponentCarrier (DL PCC) while in the uplink it is the Uplink Primary ComponentCarrier (UL PCC).

Depending on UE capabilities, Secondary Cells (SCells) can be configuredto form together with the PCell a set of serving cells. In the downlink,the carrier corresponding to an SCell is a Downlink Secondary ComponentCarrier (DL SCC), while in the uplink it is an Uplink SecondaryComponent Carrier (UL SCC).

The configured set of serving cells for a UE therefore always consistsof one PCell and one or more SCells:

-   -   For each SCell the usage of uplink resources by the UE in        addition to the downlink ones is configurable (the number of DL        SCCs configured is therefore always larger or equal to the        number of UL SCCs and no SCell can be configured for usage of        uplink resources only);    -   From a UE viewpoint, each uplink resource only belongs to one        serving cell;    -   The number of serving cells that can be configured depends on        the aggregation capability of the UE;    -   PCell can only be changed with handover procedure (i.e., with        security key change and RACH procedure);    -   PCell is used for transmission of PUCCH;    -   Unlike SCells, PCell cannot be de-activated;    -   Re-establishment is triggered when the PCell experiences        Rayleigh fading (RLF), not when SCells experience RLF;    -   Non-access stratum (NAS) information is taken from the downlink        PCell.

The configuration and reconfiguration of component carriers can beperformed by RRC. Activation and deactivation is done via MAC controlelements. At intra-LTE handover, RRC can also add, remove, orreconfigure SCells for usage in the target cell. The reconfiguration,addition and removal of SCells can be performed by RRC. At intra-LTEhandover, RRC can also add, remove, or reconfigure SCells for usage withthe target PCell. When adding a new SCell, dedicated RRC signaling isused for sending all required system information of the SCell, i.e.,while in connected mode, UEs need not acquire broadcasted systeminformation directly from the SCells.

When a user equipment is configured with carrier aggregation there isone pair of uplink and downlink component carriers that is alwaysactive. The downlink component carrier of that pair might be alsoreferred to as ‘DL anchor carrier’. Same applies also for the uplink.

When carrier aggregation is configured, a user equipment may bescheduled over multiple component carriers simultaneously but at mostone random access procedure shall be ongoing at any time. Cross-carrierscheduling allows the PDCCH of a component carrier to schedule resourceson another component carrier. For this purpose a component carrieridentification field is introduced in the respective DCI formats, calledCIF.

A linking between uplink and downlink component carriers allowsidentifying the uplink component carrier for which the grant applieswhen there is no cross-carrier scheduling. The linkage of downlinkcomponent carriers to uplink component carrier does not necessarily needto be one to one. In other words, more than one downlink componentcarrier can link to the same uplink component carrier. At the same time,a downlink component carrier can only link to one uplink componentcarrier.

LTE RRC States

The following is mainly describing the two main states in LTE:“RRC_IDLE” and “RRC_CONNECTED”.

In RRC_IDLE the radio is not active, but an ID is assigned and trackedby the network. More specifically, a mobile terminal in RRC_IDLEperforms cell selection and reselection—in other words, it decides onwhich cell to camp. The cell (re)selection process takes into accountthe priority of each applicable frequency of each applicable RadioAccess Technology (RAT), the radio link quality and the cell status(i.e., whether a cell is barred or reserved). An RRC_IDLE mobileterminal monitors a paging channel to detect incoming calls, and alsoacquires system information. The system information mainly consists ofparameters by which the network (E-UTRAN) can control the cell(re)selection process. RRC specifies the control signaling applicablefor a mobile terminal in RRC_IDLE, namely paging and system information.The mobile terminal behavior in RRC_IDLE is specified in TS 25.912,e.g., Chapter 8.4.2 incorporated herein by reference.

In RRC_CONNECTED the mobile terminal has an active radio operation withcontexts in the eNodeB. The E-UTRAN allocates radio resources to themobile terminal to facilitate the transfer of (unicast) data via shareddata channels. To support this operation, the mobile terminal monitorsan associated control channel which is used to indicate the dynamicallocation of the shared transmission resources in time and frequency.The mobile terminal provides the network with reports of its bufferstatus and of the downlink channel quality, as well as neighboring cellmeasurement information to enable E-UTRAN to select the most appropriatecell for the mobile terminal. These measurement reports include cellsusing other frequencies or RATs. The UE also receives systeminformation, consisting mainly of information required to use thetransmission channels. To extend its battery lifetime, a UE inRRC_CONNECTED may be configured with a Discontinuous Reception (DRX)cycle. RRC is the protocol by which the E-UTRAN controls the UE behaviorin RRC_CONNECTED.

Logical and Transport Channels

The MAC layer provides a data transfer service for the RLC layer throughlogical channels. Logical channels are either Control Logical Channelswhich carry control data such as RRC signaling, or Traffic LogicalChannels which carry user plane data. Broadcast Control Channel (BCCH),Paging Control channel (PCCH), Common Control Channel (CCCH), MulticastControl Channel (MCCH) and Dedicated Control Channel (DCCH) are ControlLogical Channels. Dedicated Traffic channel (DTCH) and Multicast TrafficChannel (MTCH) are Traffic Logical Channels.

Data from the MAC layer is exchanged with the physical layer throughTransport Channels. Data is multiplexed into transport channelsdepending on how it is transmitted over the air. Transport channels areclassified as downlink or uplink as follows. Broadcast Channel (BCH),Downlink Shared Channel (DL-SCH), Paging Channel (PCH) and MulticastChannel (MCH) are downlink transport channels, whereas the Uplink SharedChannel (UL-SCH) and the Random Access Channel (RACH) are uplinktransport channels.

A multiplexing is then performed between logical channels and transportchannels in the downlink and uplink respectively.

Layer 1/Layer 2 (L1/L2) Control Signaling

In order to inform the scheduled users about their allocation status,transport format and other data-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a sub-frame,assuming that the user allocation can change from sub-frame tosub-frame. It should be noted that user allocation might also beperformed on a TTI (Transmission Time Interval) basis, where the TTIlength is a multiple of the sub-frames. The TTI length may be fixed in aservice area for all users, may be different for different users, or mayeven by dynamic for each user. Generally, the L1/2 control signalingneeds only be transmitted once per TTI.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which includes resource assignments and other controlinformation for a mobile terminal or groups of UEs. In general, severalPDCCHs can be transmitted in one sub-frame.

It should be noted that in 3GPP LTE, assignments for uplink datatransmissions, also referred to as uplink scheduling grants or uplinkresource assignments, are also transmitted on the PDCCH.

With respect to scheduling grants, the information sent on the L1/L2control signaling may be separated into the following two categories,Shared Control Information (SCI) carrying Cat 1 information and DownlinkControl Information (DCI) carrying Cat 2/3 information.

Shared Control Information (SCI) Carrying Cat 1 Information

The shared control information part of the L1/L2 control signalingcontains information related to the resource allocation (indication).The shared control information typically contains the followinginformation:

-   -   A user identity indicating the user(s) that is/are allocated the        resources.    -   RB allocation information for indicating the resources (Resource        Blocks (RBs)) on which a user(s) is/are allocated. The number of        allocated resource blocks can be dynamic.    -   The duration of assignment (optional), if an assignment over        multiple sub-frames (or TTIs) is possible.

Depending on the setup of other channels and the setup of the DownlinkControl Information (DCI)—see below—the shared control information mayadditionally contain information such as ACK/NACK for uplinktransmission, uplink scheduling information, information on the DCI(resource, MCS, etc.).

Downlink Control Information (DCI) Carrying Cat 2/3 Information

The downlink control information part of the L1/L2 control signalingcontains information related to the transmission format (Cat 2information) of the data transmitted to a scheduled user indicated bythe Cat 1 information. Moreover, in case of using (Hybrid) ARQ as aretransmission protocol, the Cat 2 information carries HARQ (Cat 3)information. The downlink control information needs only to be decodedby the user scheduled according to Cat 1. The downlink controlinformation typically contains information on:

-   -   Cat 2 information: Modulation scheme, transport-block (payload)        size or coding rate, MIMO (Multiple Input Multiple        Output)-related information, etc. Either the transport-block (or        payload size) or the code rate can be signaled. In any case        these parameters can be calculated from each other by using the        modulation scheme information and the resource information        (number of allocated resource blocks);    -   Cat 3 information: HARQ related information, e.g., hybrid ARQ        process number, redundancy version, retransmission sequence        number.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in its fields. Thedifferent DCI formats that are currently defined for LTE are as followsand described in detail in 3GPP TS 36.212, “Multiplexing and channelcoding”, section 5.3.3.1 (available at http://www.3gpp.org andincorporated herein by reference).

Format 0: DCI Format 0 is used for the transmission of resource grantsfor the PUSCH.

For further information regarding the DCI formats and the particularinformation that is transmitted in the DCI, please refer to thetechnical standard or to LTE—The UMTS Long Term Evolution—From Theory toPractice, Edited by Stefania Sesia, Issam Toufik, Matthew Baker, Chapter9.3, incorporated herein by reference.

Downlink & Uplink Data Transmission

Regarding downlink data transmission, L1/L2 control signaling istransmitted on a separate physical channel (PDCCH), along with thedownlink packet data transmission. This L1/L2 control signalingtypically contains information on:

-   -   The physical resource(s) on which the data is transmitted (e.g.,        subcarriers or subcarrier blocks in case of OFDM, codes in case        of CDMA). This information allows the mobile terminal (receiver)        to identify the resources on which the data is transmitted.    -   When user equipment is configured to have a Carrier Indication        Field (CIF) in the L1/L2 control signaling, this information        identifies the component carrier for which the specific control        signaling information is intended. This enables assignments to        be sent on one component carrier which are intended for another        component carrier (“cross-carrier scheduling”). This other,        cross-scheduled component carrier could be for example a        PDCCH-less component carrier, i.e., the cross-scheduled        component carrier does not carry any L1/L2 control signaling.    -   The Transport Format, which is used for the transmission. This        can be the transport block size of the data (payload size,        information bits size), the MCS (Modulation and Coding Scheme)        level, the Spectral Efficiency, the code rate, etc. This        information (usually together with the resource allocation        (e.g., the number of resource blocks assigned to the user        equipment)) allows the user equipment (receiver) to identify the        information bit size, the modulation scheme and the code rate in        order to start the demodulation, the de-rate-matching and the        decoding process. The modulation scheme may be signaled        explicitly.    -   Hybrid ARQ (HARQ) information:        -   HARQ process number: Allows the user equipment to identify            the hybrid ARQ process on which the data is mapped.        -   Sequence number or new data indicator (NDI): Allows the user            equipment to identify if the transmission is a new packet or            a retransmitted packet. If soft combining is implemented in            the HARQ protocol, the sequence number or new data indicator            together with the HARQ process number enables soft-combining            of the transmissions for a PDU prior to decoding.        -   Redundancy and/or constellation version: Tells the user            equipment, which hybrid ARQ redundancy version is used            (required for de-rate-matching) and/or which modulation            constellation version is used (required for demodulation).    -   UE Identity (UE ID): Tells which user equipment the L1/L2        control signaling is intended for. In typical implementations        this information is used to mask the CRC of the L1/L2 control        signaling in order to prevent other user equipment to read this        information.

To enable an uplink packet data transmission, L1/L2 control signaling istransmitted on the downlink (PDCCH) to tell the user equipment about thetransmission details. This L1/L2 control signaling typically containsinformation on:

-   -   The physical resource(s) on which the user equipment should        transmit the data (e.g., subcarriers or subcarrier blocks in        case of OFDM, codes in case of CDMA).    -   When user equipment is configured to have a Carrier Indication        Field (CIF) in the L1/L2 control signaling, this information        identifies the component carrier for which the specific control        signaling information is intended. This enables assignments to        be sent on one component carrier which are intended for another        component carrier. This other, cross-scheduled component carrier        may be for example a PDCCH-less component carrier, i.e., the        cross-scheduled component carrier does not carry any L1/L2        control signaling.    -   L1/L2 control signaling for uplink grants is sent on the DL        component carrier that is linked with the uplink component        carrier or on one of the several DL component carriers, if        several DL component carriers link to the same UL component        carrier.    -   The Transport Format, the user equipment should use for the        transmission. This can be the transport block size of the data        (payload size, information bits size), the MCS (Modulation and        Coding Scheme) level, the Spectral Efficiency, the code rate,        etc. This information (usually together with the resource        allocation (e.g., the number of resource blocks assigned to the        user equipment)) allows the user equipment (transmitter) to pick        the information bit size, the modulation scheme and the code        rate in order to start the modulation, the rate-matching and the        encoding process. In some cases the modulation scheme may be        signaled explicitly.    -   Hybrid ARQ information:        -   HARQ Process number: Tells the user equipment from which            hybrid ARQ process it should pick the data.        -   Sequence number or new data indicator: Tells the user            equipment to transmit a new packet or to retransmit a            packet. If soft combining is implemented in the HARQ            protocol, the sequence number or new data indicator together            with the HARQ process number enables soft-combining of the            transmissions for a protocol data unit (PDU) prior to            decoding.        -   Redundancy and/or constellation version: Tells the user            equipment which hybrid ARQ redundancy version to use            (required for rate-matching) and/or which modulation            constellation version to use (required for modulation).    -   UE Identity (UE ID): Tells which user equipment should transmit        data. In typical implementations this information is used to        mask the CRC of the L1/L2 control signaling in order to prevent        other user equipment to read this information.

There are several different possibilities how to exactly transmit theinformation pieces mentioned above in uplink and downlink datatransmission. Moreover, in uplink and downlink, the L1/L2 controlinformation may also contain additional information or may omit some ofthe information. For example:

-   -   HARQ process number may not be needed, i.e., is not signaled, in        case of a synchronous HARQ protocol.    -   A redundancy and/or constellation version may not be needed, and        thus not signaled, if Chase Combining is used (always the same        redundancy and/or constellation version) or if the sequence of        redundancy and/or constellation versions is pre-defined.    -   Power control information may be additionally included in the        control signaling.    -   MIMO related control information, such as, e.g., pre-coding, may        be additionally included in the control signaling.    -   In case of multi-code word MIMO transmission transport format        and/or HARQ information for multiple code words may be included.

For uplink resource assignments (on the Physical Uplink Shared Channel(PUSCH)) signaled on PDCCH in LTE, the L1/L2 control information doesnot contain a HARQ process number, since a synchronous HARQ protocol isemployed for LTE uplink. The HARQ process to be used for an uplinktransmission is given by the timing. Furthermore, it should be notedthat the redundancy version (RV) information is jointly encoded with thetransport format information, i.e., the RV info is embedded in thetransport format (TF) field. The Transport Format (TF) respectivelymodulation and coding scheme (MCS) field has, for example, a size of 5bits, which corresponds to 32 entries. Three TF/MCS table entries arereserved for indicating redundancy versions (RVs) 1, 2 or 3. Theremaining MCS table entries are used to signal the MCS level (TBS)implicitly indicating RV0. The size of the CRC field of the PDCCH is 16bits.

For downlink assignments (PDSCH) signaled on PDCCH in LTE the RedundancyVersion (RV) is signaled separately in a two-bit field. Furthermore, themodulation order information is jointly encoded with the transportformat information. Similar to the uplink case there is 5 bit MCS fieldsignaled on PDCCH. Three of the entries are reserved to signal anexplicit modulation order, providing no Transport format (Transportblock) info. For the remaining 29 entries modulation order and Transportblock size info are signaled.

Uplink Access Scheme for LTE

For Uplink transmission, power-efficient user-terminal transmission isnecessary to maximize coverage. Single-carrier transmission combinedwith FDMA with dynamic bandwidth allocation has been chosen as theevolved UTRA uplink transmission scheme. The main reason for thepreference for single-carrier transmission is the lower peak-to-averagepower ratio (PAPR), compared to multi-carrier signals (OFDMA), and thecorresponding improved power-amplifier efficiency and assumed improvedcoverage (higher data rates for a given terminal peak power). Duringeach time interval, Node B assigns users a unique time/frequencyresource for transmitting user data thereby ensuring intra-cellorthogonality. An orthogonal access in the uplink promises increasedspectral efficiency by eliminating intra-cell interference. Interferencedue to multipath propagation is handled at the base station (Node B),aided by insertion of a cyclic prefix in the transmitted signal.

The basic physical resource used for data transmission consists of afrequency resource of size BW_(grant) during one time interval, e.g., asub-frame of 0.5 ms, onto which coded information bits are mapped. Itshould be noted that a sub-frame, also referred to as transmission timeinterval (TTI), is the smallest time interval for user datatransmission. It is, however, possible to assign a frequency resourceBW_(grant) over a longer time period than one TTI to a user byconcatenation of sub-frames.

Uplink Scheduling Scheme for LTE

The uplink scheme allows for both scheduled access, i.e., controlled byeNB, and contention-based access.

In case of scheduled access, the UE is allocated a certain frequencyresource for a certain time (i.e., a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access; within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is, for example, the randomaccess, i.e., when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access the Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines

-   -   which UE(s) that is (are) allowed to transmit,    -   which physical channel resources (frequency),    -   Transport format (Modulation Coding Scheme (MCS)) to be used by        the mobile terminal for transmission

The allocation information is signaled to the UE via a scheduling grant,sent on the L1/L2 control channel. For simplicity reasons this channelmay be called uplink grant channel in the following. A scheduling grantmessage contains at least information which part of the frequency bandthe UE is allowed to use, the validity period of the grant and thetransport format the UE has to use for the upcoming uplink transmission.The shortest validity period is one sub-frame. Additional informationmay also be included in the grant message, depending on the selectedscheme. Only “per UE” grants are used to grant the right to transmit onthe UL-SCH (i.e., there are no “per UE per RB” grants). Therefore, theUE needs to distribute the allocated resources among the radio bearersaccording to some rules. Unlike in HSUPA there is no UE-based transportformat selection. The eNB decides the transport format based on someinformation, e.g., reported scheduling information and QoS info, and UEhas to follow the selected transport format. In HSUPA the Node B assignsthe maximum uplink resource, and the UE selects accordingly the actualtransport format for the data transmissions.

Since the scheduling of radio resources is the most important functionin a shared channel access network for determining Quality of service,there are a number of requirements that should be fulfilled by the ULscheduling scheme for LTE in order to allow for an efficient QoSmanagement.

-   -   Starvation of low priority services should be avoided;    -   Clear QoS differentiation for radio bearers/services should be        supported by the scheduling scheme;    -   The UL reporting should allow fine granular buffer status        reports (e.g., per radio bearer or per radio bearer group) in        order to allow the eNB scheduler to identify for which Radio        Bearer/service data is to be sent;    -   It should be possible to make clear QoS differentiation between        services of different users;    -   It should be possible to provide a minimum bit rate per radio        bearer.

As can be seen from the above list, one essential aspect of the LTEscheduling scheme is to provide mechanisms with which the operator cancontrol the partitioning of its aggregated cell capacity between theradio bearers of the different QoS classes. The QoS class of a radiobearer is identified by the QoS profile of the corresponding SAE bearersignaled from AGW to eNB as described before. An operator can thenallocate a certain amount of its aggregated cell capacity to theaggregated traffic associated with radio bearers of a certain QoS class.The main goal of employing this class-based approach is to be able todifferentiate the treatment of packets depending on the QoS class theybelong to.

Buffer Status Reporting/Scheduling Request Procedure for UplinkScheduling

The usual mode of scheduling is dynamic scheduling, by means of downlinkassignment messages for the allocation of downlink transmissionresources and uplink grant messages for the allocation of uplinktransmission resources; these are usually valid for specific singlesub-frames. They are transmitted on the PDCCH using C-RNTI of the UE asalready mentioned before. Dynamic scheduling is efficient for servicestypes, in which the traffic is bursty and dynamic in rate, such as TCP.

In addition to the dynamic scheduling, a persistent scheduling isdefined, which enables radio resources to be semi-statically configuredand allocated to a UE for a longer time period than one sub-frame, thusavoiding the need for specific downlink assignment messages or uplinkgrant messages over the PDCCH for each sub-frame. Persistent schedulingis useful for services such as VoIP for which the data packets aresmall, periodic and semi-static in size. Thus, the overhead of the PDCCHis significantly reduced compared to the case of dynamic scheduling.

Buffer status reports (BSR) from the UE to the eNodeB are used to assistthe eNodeB in allocating uplink resources, i.e., uplink scheduling. Forthe downlink case, the eNB scheduler is obviously aware of the amount ofdata to be delivered to each UE; however, for the uplink direction,since scheduling decisions are done at the eNB and the buffer for thedata is in the UE, BSRs have to be sent from the UE to the eNB in orderto indicate the amount of data that needs to be transmitted over theUL-SCH.

There are basically two types of Buffer Status Report MAC controlelements (BSR) defined for LTE: a long BSR (with four buffer size fieldscorresponding to LCG IDs #0-3) or a short BSR (with one LCG ID field andone corresponding buffer size field). The buffer size field indicatesthe total amount of data available across all logical channels of alogical channel group, and is indicated in number of bytes encoded as anindex of different buffer size levels (see also 3GPP TS 36.321 v 10.5.0Chapter 6.1.3.1, incorporated herewith by reference). In addition, thereis a further type of Buffer Status Report, for use of truncated data,where the Buffer Status Report is 2 bytes long.

Which one of either the short or the long BSR is transmitted by the UEdepends on the available transmission resources in a transport block, onhow many groups of logical channels have non-empty buffers and onwhether a specific event is triggered at the UE. The long BSR reportsthe amount of data for four logical channel groups, whereas the shortBSR indicates the amount of data buffered for only the highest logicalchannel group.

The reason for introducing the logical channel group concept is thateven though the UE may have more than four logical channels configured,reporting the buffer status for each individual logical channel wouldcause too much signaling overhead. Therefore, the eNB assigns eachlogical channel to a logical channel group; preferably, logical channelswith same/similar QoS requirements should be allocated within the samelogical channel group.

A BSR may be triggered, as an example, for the following events:

-   -   Whenever data arrives for a logical channel, which has a higher        priority than the logical channels whose buffer are non-empty;    -   Whenever data becomes available for any logical channel, when        there was previously no data available for transmission;    -   Whenever the retransmission BSR time expires;    -   Whenever periodic BSR reporting is due, i.e., periodic BSR timer        expires;    -   Whenever there is a spare space in a transport block which can        accommodate a BSR.

In order to be robust against transmission failures, there is a BSRretransmission mechanism defined for LTE; the retransmission BSR timeris started or restarted whenever an uplink grant is restarted. If nouplink grant is received before the retransmission BSR timer expires,another BSR is triggered by the UE.

If the UE has no uplink resources allocated for including a BSR in thetransport block (TB) when a BSR is triggered the UE sends a schedulingrequest (SR) on the Physical Uplink Control Channel (PUCCH), ifconfigured. For the case that there are no D-SR (dedicated Schedulingrequest) resources on PUCCH configured, the UE will start the RandomAccess Procedure (RACH procedure) in order to request UL-SCH resourcesfor transmission the BSR info to eNB. However, it should be noted thatthe UE will not trigger SR transmission for the case that a periodic BSRis to be transmitted.

Furthermore an enhancement to the SR transmission has been introducedfor a specific scheduling mode where resources are persistentlyallocated with a defined periodicity in order to save L1/2 controlsignaling overhead for transmission grants, which is referred to assemi-persistent scheduling (SPS). One example for a service, which hasbeen mainly considered for semi-persistent scheduling is VoIP. Every 20ms a VoIP packet is generated at the Codec during a talk-spurt.Therefore eNB can allocate uplink or respectively downlink resourcepersistently every 20 ms, which could be then used for the transmissionof VoIP packets. In general SPS is beneficial for services withpredictable traffic behavior, i.e., constant bit rate, packet arrivaltime is periodic. For the case that SPS is configured for the uplinkdirection, the eNB can turn off SR triggering/transmission for certainconfigured logical channels, i.e., BSR triggering due to data arrival onthose specific configured logical channels will not trigger an SR. Themotivation for such kind of enhancements is reporting an SR for thoselogical channels which will use the semi-persistently allocatedresources (logical channels which carry VoIP packets) is of no value foreNB scheduling and hence should be avoided.

More detailed information with regard to BSR and in particular thetriggering of same is explained in 3GPP TS 36.321 V10.5 in Chapter 5.4.5incorporated herewith by reference.

Logical Channel Prioritization

The UE has an uplink rate control function which manages the sharing ofuplink resources between radio bearers. This uplink rate controlfunction is also referred to as logical channel prioritization procedurein the following. The Logical Channel Prioritization (LCP) procedure isapplied when a new transmission is performed, i.e., a Transport blockneeds to be generated. One proposal for assigning capacity has been toassign resources to each bearer, in priority order, until each hasreceived an allocation equivalent to the minimum data rate for thatbearer, after which any additional capacity is assigned to bearers in,for example, priority order.

As will become evident from the description of the LCP procedure givenbelow, the implementation of the LCP procedure residing in the UE isbased on the token bucket model, which is well known in the IP world.The basic functionality of this model is as follows. Periodically at agiven rate a token, which represents the right to transmit a quantity ofdata, is added to the bucket. When the UE is granted resources, it isallowed to transmit data up to the amount represented by the number oftokens in the bucket. When transmitting data the UE removes the numberof tokens equivalent to the quantity of transmitted data. In case thebucket is full, any further tokens are discarded. For the addition oftokens it could be assumed that the period of the repetition of thisprocess would be every TTI, but it could be easily lengthened such thata token is only added every second. Basically instead of every 1 ms atoken is added to the bucket, 1000 tokens could be added every second.In the following the logical channel prioritization procedure which isused in Rel-8 is described.

More detailed information with regard to the LCP procedure is explainedin 3GPP TS 36.321 V8 in Chapter 5.4.3.1, incorporated herewith byreference.

RRC controls the scheduling of uplink data by signaling for each logicalchannel: priority where an increasing priority value indicates a lowerpriority level, prioritisedBitRate which sets the Prioritized Bit Rate(PBR), bucketSizeDuration which sets the Bucket Size Duration (BSD). Theidea behind prioritized bit rate is to support for each bearer,including low priority non-GBR bearers, a minimum bit rate in order toavoid a potential starvation. Each bearer should at least get enoughresources in order to achieve the prioritized bit rate (PRB).

The UE shall maintain a variable Bj for each logical channel j. Bj shallbe initialized to zero when the related logical channel is established,and incremented by the product PBR×TTI duration for each TTI, where PBRis Prioritized Bit Rate of logical channel j. However, the value of Bjcan never exceed the bucket size and if the value of Bj is larger thanthe bucket size of logical channel j, it shall be set to the bucketsize. The bucket size of a logical channel is equal to PBR×BSD, wherePBR and BSD are configured by upper layers.

The UE shall perform the following Logical Channel Prioritizationprocedure when a new transmission is performed:

-   -   The UE shall allocate resources to the logical channels in the        following steps:    -   Step 1: All the logical channels with Bj>0 are allocated        resources in a decreasing priority order. If the PBR of a radio        bearer is set to “infinity”, the UE shall allocate resources for        all the data that is available for transmission on the radio        bearer before meeting the PBR of the lower priority radio        bearer(s);    -   Step 2: the UE shall decrement Bj by the total size of MAC SDUs        served to logical channel j in Step 1 It has to be noted at this        point that the value of Bj can be negative.    -   Step 3: if any resources remain, all the logical channels are        served in a strict decreasing priority order (regardless of the        value of Bj) until either the data for that logical channel or        the UL grant is exhausted, whichever comes first. Logical        channels configured with equal priority should be served        equally.    -   The UE shall also follow the rules below during the scheduling        procedures above:    -   the UE should not segment an RLC SDU (or partially transmitted        SDU or retransmitted RLC PDU) if the whole SDU (or partially        transmitted SDU or retransmitted RLC PDU) fits into the        remaining resources;    -   if the UE segments an RLC SDU from the logical channel, it shall        maximize the size of the segment to fill the grant as much as        possible;    -   UE should maximize the transmission of data.

For the Logical Channel Prioritization procedure, the UE shall take intoaccount the following relative priority in decreasing order:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for PHR;    -   data from any Logical Channel, except data from UL-CCCH;    -   MAC control element for BSR included for padding.

For the case of carrier aggregation, which is described in a latersection, when the UE is requested to transmit multiple MAC PDUs in oneTTI, steps 1 to 3 and the associated rules may be applied either to eachgrant independently or to the sum of the capacities of the grants. Alsothe order in which the grants are processed is left up to UEimplementation. It is up to the UE implementation to decide in which MACPDU a MAC control element is included when UE is requested to transmitmultiple MAC PDUs in one TTI.

Uplink Power Control

Uplink transmission power control in a mobile communication systemserves an important purpose: it balances the need for sufficienttransmitted energy per bit to achieve the required Quality-of-Service(QoS), against the needs to minimize interference to other users of thesystem and to maximize the battery life of the mobile terminal. Inachieving this purpose, the role of the Power Control (PC) becomesdecisive to provide the required SINR while controlling at the same timethe interference caused to neighboring cells. The idea of classic PCschemes in uplink is that all users are received with the same SINR,which is known as full compensation. As an alternative, 3GPP has adoptedfor LTE the use of Fractional Power Control (FPC). This newfunctionality makes users with a higher path-loss operate at a lowerSINR requirement so that they will more likely generate lessinterference to neighboring cells.

Detailed power control formulae are specified in LTE for the PhysicalUplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH)and the Sounding Reference Signals (SRSs) (section 5.1 in TS36.213). Theformula for each of these uplink signals follows the same basicprinciples; in all cases they can be considered as a summation of twomain terms: a basic open-loop operating point derived from static orsemi-static parameters signaled by the eNodeB, and a dynamic offsetupdated from sub-frame to sub-frame.

The basic open-loop operating point for the transmit power per resourceblock depends on a number of factors including the inter-cellinterference and cell load. It can be further broken down into twocomponents, a semi-static base level P0, further comprised of a commonpower level for all UEs in the cell (measured in dBm) and a UE-specificoffset, and an open-loop path-loss compensation component. The dynamicoffset part of the power per resource block can also be further brokendown into two components, a component dependent on the used MCS andexplicit Transmitter Power Control (TPC) commands.

The MCS-dependent component (referred to in the LTE specifications asATF, where TF stands for ‘Transport Format’) allows the transmittedpower per RB to be adapted according to the transmitted information datarate.

The other component of the dynamic offset is the UE-specific TPCcommands. These can operate in two different modes: accumulative TPCcommands (available for PUSCH, PUCCH and SRS) and absolute TPC commands(available for PUSCH only). For the PUSCH, the switch between these twomodes is configured semi-statically for each UE by RRC signaling—i.e.,the mode cannot be changed dynamically. With the accumulative TPCcommands, each TPC command signals a power step relative to the previouslevel.

Power Headroom Reporting

In order to assist the eNodeB to schedule the uplink transmissionresources to different UEs in an appropriate way, it is important thatthe UE can report its available power headroom to eNodeB.

The eNodeB can use the power headroom reports to determine how much moreuplink bandwidth per sub-frame a UE is capable of using. This helps toavoid allocating uplink transmission resources to UEs which are unableto use them in order to avoid a waste of resources.

The range of the power headroom report is from +40 to −23 dB. Thenegative part of the range enables the UE to signal to the eNodeB theextent to which it has received an UL grant which would require moretransmission power than the UE has available. This would enable theeNodeB to reduce the size of a subsequent grant, thus freeing uptransmission resources to allocate to other UEs.

A power headroom report can only be sent in sub-frames in which a UE hasan UL grant. The report relates to the sub-frame in which it is sent. Anumber of criteria are defined to trigger a power headroom report. Theseinclude:

-   -   A significant change in estimated path loss since the last power        headroom report    -   More than a configured time has elapsed since the previous power        headroom report    -   More than a configured number of closed-loop TPC commands have        been implemented by the UE

The eNodeB can configure parameters to control each of these triggersdepending on the system loading and the requirements of its schedulingalgorithm. To be more specific, RRC controls power headroom reporting byconfiguring the two timers periodicPHR-Timer and prohibitPHR-Timer, andby signaling dl-PathlossChange which sets the change in measureddownlink pathloss to trigger a power headroom report.

The power headroom report is send as a MAC Control Element. It consistsof a single octet where the two highest bits are reserved and the sixlowest bits represent the dB values mentioned above in 1 dB steps. Thestructure of the MAC Control Element is shown in FIG. 7.

The UE power headroom PH valid for sub-frame i is defined by:

PH(i)=P _(CMAX)−{10 log₁₀(M _(PUSCH)(i))+P _(O) _(_)_(PUSCH)(j)+α(j)·PL|Δ _(TF)(i)+f(i)} [dB]

The power headroom shall be rounded to the closest value in the range[40; −23] dB with steps of 1 dB.

P_(cmax), the maximum UE Transmission power (Tx power) is a value chosenby the UE in the given range of P_(CMAX) _(_) _(L) and P_(CMAX) _(_)_(H).

P _(CMAX) _(_) _(L) ≤P _(CMAX) ≤P _(CMAX) _(_) _(H), where

P _(CMAX) _(_) _(L)=MIN{P _(EMAX) −ΔT _(C) ,P _(PowerClass)−MPR−A-MPR−ΔT _(c)}, and

P _(CMAX) _(_) _(H)=MIN{P _(EMAX) ,P _(PowerClass)};

And where P_(EMAX) is the value signaled by the network.

MPR is a power reduction value used to control the adjacent channelleakage power ratio (ACLR) associated with the various modulationschemes and the transmission bandwidth.

A-MPR is the additional maximum power reduction. It is band specific andit is applied when configured by the network. Therefore, Pcmax is UEimplementation specific and hence not known by eNB.

More detailed information with regard to ΔT_(C) is specified in 3GPP TSTS36.101, Vers. 12.0.0, section 6.2.5, incorporated herein by reference.

LTE Device-to-Device (D2D) Proximity Services

Proximity-based applications and services represent an emergingsocial-technological trend. The identified areas include servicesrelated to commercial services and Public Safety that would be ofinterest to operators and users. The introduction of a ProximityServices (ProSe) capability in LTE would allow the 3GPP industry toserve this developing market, and will, at the same time, serve theurgent needs of several Public Safety communities that are jointlycommitted to LTE.

Device-to-Device (D2D) communication is a technology component forLTE-rel.12. The Device-to-Device (D2D) communication technology allowsD2D as an underlay to the cellular network to increase the spectralefficiency. For example, if the cellular network is LTE, all datacarrying physical channels use SC-FDMA for D2D signaling. In D2Dcommunication, user equipment (UEs) transmit data signals to each otherover a direct link using the cellular resources instead of through theBase Station. A possible scenario in a D2D compatible communicationsystem is shown in FIG. 9.

D2D Communication in LTE

The “D2D communication in LTE” is focusing on two areas; Discovery andCommunication whereas this invention is mostly related to thecommunication part. Therefore in the following the technical backgroundis focusing on the communication part.

Device-to-Device (D2D) communication is a technology component forLTE-A. In D2D communication, UEs transmit data signals to each otherover a direct link using the cellular resources instead of through theBS. D2D users communicate directly while remaining controlled under theBS, i.e., at least when being in coverage of an eNB. Therefore D2D canimprove system performances by reusing cellular resources.

It is assumed that D2D operates in uplink LTE spectrum (in the case ofFDD) or uplink sub-frames of the cell giving coverage (in case of TDDexcept when out of coverage). Furthermore D2D transmission/receptiondoes not use full duplex on a given carrier. From individual UEperspective, on a given carrier D2D signal reception and LTE uplinktransmission do not use full duplex, i.e., no simultaneous D2D signalreception and LTE UL transmission is possible.

In D2D communication when UE1 has a role of transmission (transmittinguser equipment), UE1 sends data and UE2 (receiving user equipment)receives it. UE1 and UE2 can change their transmission and receptionrole. The transmission from UE1 can be received by one or more UEs likeUE2.

With respect to the User plane protocols, in the following the contentof the agreement [3GPP TS 36.843vers. 12.0.0 section 9.2] from D2Dcommunication perspective is reported:

-   -   PDCP:        -   1: M D2D broadcast communication data (i.e., IP packets)            should be handled as the normal user-plane data.        -   Header-compression/decompression in PDCP is applicable for            1: M D2D broadcast communication.        -   U-Mode is used for header compression in PDCP for D2D            broadcast operation for public safety;    -   RLC:        -   RLC UM is used for 1: M D2D broadcast communication.        -   Segmentation and Re-assembly is supported on L2 by RLC UM.        -   A receiving UE needs to maintain at least one RLC UM entity            per transmitting peer UE.        -   An RLC UM receiver entity does not need to be configured            prior to reception of the first RLC UM data unit.        -   So far no need has been identified for RLC AM or RLC TM for            D2D communication for user plane data transmission.    -   MAC:        -   No HARQ feedback is assumed for 1: M D2D broadcast            communication        -   The receiving UE needs to know a source ID in order to            identify the receiver RLC UM entity.        -   The MAC header comprises a L2 target ID which allows            filtering out packets at MAC layer.        -   The L2 target ID may be a broadcast, group cast or unicast            address.            -   L2 Groupcast/Unicast: A L2 target ID carried in the MAC                header would allow discarding a received RLC UM PDU even                before delivering it to the RLC receiver entity.            -   L2 Broadcast: A receiving UE would process all received                RLC PDUs from all transmitters and aim to re-assemble                and deliver IP packets to upper layers.        -   MAC sub header contains LCIDs (to differentiate multiple            logical channels).        -   At least Multiplexing/de-multiplexing, priority handling and            padding are useful for D2D.

Resource Allocation

The resource allocation for D2D communication is under discussion and isdescribed in its present form in 3GPP TS 36.843, version 12.0.0, section9.2.3, incorporated herein by reference.

From the perspective of a transmitting UE, a UE can operate in two modesfor resource allocation:

-   -   Mode 1: eNodeB or Release-10 relay node schedules the exact        resources used by a UE to transmit direct data and direct        control information    -   Mode 2: a UE on its own selects resources from resource pools to        transmit direct data and direct control information

D2D communication capable UE shall support at least Mode 1 forin-coverage. D2D communication capable UE shall support Mode 2 for atleast edge-of-coverage and/or out-of-coverage

UEs in-coverage and out-of-coverage need to be aware of a resource pool(time/frequency) for D2D communication reception.

All UEs (Mode 1 (“scheduled”) and Mode 2 (“autonomous”)) are providedwith a resource pool (time and frequency) in which they attempt toreceive scheduling assignments.

In Mode 1, a UE requests transmission resources from an eNodeB. TheeNodeB schedules transmission resources for transmission of schedulingassignment(s) and data.

-   -   The UE sends a scheduling request (D-SR or RA) to the eNodeB        followed by a BSR based on which the eNodeB can determine that        the UE intends to perform a D2D transmission as well as the        required amount resources.    -   In Mode 1, the UE needs to be RRC Connected in order to transmit        D2D communication.

For Mode 2, UEs are provided with a resource pool (time and frequency)from which they choose resources for transmitting D2D communication.

FIG. 8 schematically illustrates the Overlay (LTE) and the Underlay(D2D) transmission and/or reception resources. The eNodeB controlswhether the UE may apply Mode 1 or Mode 2 transmission. Once the UEknows its resources where it can transmit (or receive) D2Dcommunication, it uses the corresponding resources only for thecorresponding transmission/reception. In the example of FIG. 8, the D2Dsub-frames will only be used to receive or transmit the D2D signals.Since the UE as a D2D device would operate in Half Duplex mode, it caneither receive or transmit the D2D signals at any point of time.Similarly, in the same figure, the other sub-frames can be used for LTE(overlay) transmissions and/or reception.

D2D discovery is the procedure/process of identifying other D2D capableand interested devices in the vicinity. For this purpose, the D2Ddevices that want to be discovered would send some discovery signals (oncertain network resources) and the receiving UE interested in the saiddiscovery signal will come to know of such transmitting D2D devices. Ch.8 of 3GPP TS 36.843 describes the available details of D2D Discoverymechanisms. Following two types of discovery procedure are defined:

-   -   Type 1: a discovery procedure where resources for discovery        signal transmission are allocated on a non UE specific basis    -   Type 2: a discovery procedure where resources for discovery        signal transmission are allocated on a per UE specific basis:        -   Type 2A: Resources are allocated for each specific            transmission instance of discovery signals;        -   Type 2B: Resources are semi-persistently allocated for            discovery signal transmission.

Current discussions on scheduling schemes for allocating D2D resourcesfocus on how to incorporate the D2D related SR/BSR signaling into theLTE-A system, i.e., whether LTE BSR/SR mechanism and resources, e.g.,D-SR on PUCCH or PRACH resources, are reused for D2D communicationpurpose. According to a scheme being actually considered, the eNodeBconfigures dedicated or contention-based resources within the D2Dsub-frame or region for performing the scheduling procedure. In otherwords, a scheduling request (SR) and or a Buffer Status Report (BSR)related to D2D transmissions are sent to the eNodeB on dedicatedresources on a sub-frame dedicated for D2D transmissions. Thus, the userequipment shall only use resources within D2D sub-frame/region for allthe D2D related transmissions, including messages for performing thescheduling procedure, i.e., the SR and or BSR.

This approach has the disadvantage that the radio resource managementcan get very complex when eNodeB has to support resources, such as PUCCHresources for a dedicated Scheduling Request (D-SR) and RACH resources(contention-based SR) within the D2D sub-frame or region.

As a consequence, these resources need to be also signaled to allD2D-enabled UEs and cannot be used for D2D data discovery transmission,thereby leading to a loss of performance in data transmission. Further,other modification to the LTE standard (RAN 4) will be required if newPUCCH resources are to be configured within D2D sub-frames.

Finally, the eNodeB would be required to monitor and or receive D2Dresources in order receive D-SR/PRACH/BSR from D2D UE. This solutionwould therefore lead to an overloading of the eNodeB.

SUMMARY OF THE INVENTION

In order to integrate D2D communication into the LTE system some aspectsof the LTE systems, such as the procedures, the spectrum for the datacommunication and the like are taken over. As an Example, in uplinkcommunication, the uplink spectrum of the LTE system is used also fordevice-to-device communications.

The object of the invention is developing a method and system capable ofintegrating device-to-device (D2D) communication into the LTE system ina manner so as to need as few changes as possible to the current system.More specifically, the present invention aims at developing a system anda method that incorporates the scheduling request and the Buffest StatusSupport (BSR) procedure for device-to-device communications in an LTEsystem.

The object is solved by the subject matter of the independent claims.Advantageous embodiments are subject to the dependent claims.

According to a first aspect of the present invention, a D2D capabletransmitting user equipment, which needs to transmit data to a receivinguser equipment over a direct link data channel, uses the services of theeNodeB in order to have resources allocated for transmitting said data.To this end the UE sends to the eNB scheduling information usingresources of a sub-frame dedicated for standard uplink communicationthrough the eNodeB, rather than using resources on the sub-framededicated to D2D data transmission. In order to allow the eNB todistinguish whether the received scheduling request is for allocatingresources for transmitting data over the direct link channel or over theeNB, UE may send along with the scheduling information alsoidentification information associated to the scheduling information.

Advantageously, the user equipment may send a buffer status report tothe eNodeB on the uplink data channel, for example the PUSCH, and on aframe used for LTE data transfer and scheduling messaging.

According to a further aspect of the invention, in the case that noresources are available to the UE for sending the schedulinginformation, before sending the scheduling information, the UE may sendto the eNB a scheduling request for requesting allocation of resourcesfor the uplink data channel for sending the scheduling information tothe eNB. The transmission of the scheduling request may be triggered bytwo events. The first triggering condition includes the presence of datato be transmitted in the transmission buffer of the transmitting userequipment. The second triggering condition foresees that the data in thetransmission buffer change by a predefined amount from the transmissionof the last scheduling information. Advantageously, the data in thetransmission buffer may increase by a predefined amount with respect tothe data amount in the transmission buffer at the time the lastscheduling information was triggered or sent. According to a furtheradvantageous implementation, the second triggering condition may inalternative be verified, if the data in the transmission buffer exceed apredefined threshold.

According to the first aspect described above, a transmitting userequipment is provided, which is adapted to transmit data to a receivinguser equipment over a direct link connection in a communication system.The transmitting user equipment is further adapted to request resourcesin the communication system and comprises a transmitting unit configuredto transmit to a base station direct link scheduling information forallocation of resources for transmitting data to the receiving userequipment over the direct link connection. The direct link schedulinginformation is transmitted to the base station on an uplink data channelfor transmitting data to the base station.

According to a further aspect of the invention described above, acommunication method is provided for requesting resources by atransmitting user equipment in a communication system, wherein data isto be transmitted from the transmitting user equipment to a receivinguser equipment over a direct link. The method comprises the steps oftransmitting, at the transmitting user equipment, to a base stationdirect link scheduling information for allocation of resources fortransmitting data to the receiving user equipment over the direct linkconnection. The direct link scheduling information may be transmitted tothe base station on an uplink data channel for transmitting data to thebase station.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is described in more detail in referenceto the attached figures and drawings. Similar or corresponding detailsin the figures are marked with the same reference numerals.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE;

FIG. 3 shows exemplary sub-frame boundaries on a downlink componentcarrier as defined for 3GPP LTE (Release 8/9);

FIG. 4 shows an exemplary downlink resource grid of a downlink slot asdefined for 3GPP LTE (Release 8/9);

FIGS. 5 and 6 show the 3GPP LTE-A (Release 10) Layer 2 structure withactivated carrier aggregation for the downlink and uplink, respectively;

FIG. 7 shows the structure of a MAC Control Element;

FIG. 8 is a schematic illustration showing the overlay (LTE) and theUnderlay (D2D) transmission and reception resources in D2D sub-frames;

FIG. 9 is a schematic illustration showing a system including D2Dcapable user equipment;

FIG. 10 is a schematic drawing illustrating the messages exchangedbetween the transmitting user equipment (UE1) and the base station (eNB)for scheduling purposes and the data exchange between the transmittinguser equipment (UE1) and a receiving user equipment (UE2), according toa first realization of the present invention;

FIG. 11 illustrates a composition of a MAC Protocol Data Unit (PDU)according to an implementation of the scheduling method and systemaccording to the invention;

FIG. 12 is a schematic drawing illustrating the messages exchangedbetween the transmitting user equipment (UE1) and the base station (eNB)for scheduling purposes and the data exchange between the transmittinguser equipment (UE1) and a receiving user equipment (UE2), according toa second realization of the present invention;

FIG. 13 is a flow chart illustrating the messages exchanged between thetransmitting user equipment (UE1) and the base station (eNB) forscheduling purposes and the data exchange between the transmitting userequipment (UE1) and a receiving user equipment (UE2), according to asecond realization of the present invention;

FIG. 14 is a flow chart describing reception of D2D Discovery Signals;

FIG. 15 is a schematic drawing illustrating Neighbor Discovery.

DETAILED DESCRIPTION

The following paragraphs will describe various embodiments of theinvention. For exemplary purposes only, most of the embodiments areoutlined in relation to a radio access scheme according to 3GPP LTE(Release 8/9) and LTE-A (Release 10/11/12) mobile communication systems,partly discussed in the Technical Background section above. It should benoted that the invention may be advantageously used for example in amobile communication system such as 3GPP LTE-A (Release 10/11/12)communication systems as described in the Technical Background sectionabove, but the invention is not limited to its use in this particularexemplary communication networks.

The term “direct link” used in the claims and in the description is tobe understood as a communication link (communication channel) betweentwo D2D user equipment, which allows the exchange of data directlywithout the involvement of the network. In other words, a communicationchannel is established between two user equipment in the communicationsystem, which are close enough for directly exchanging data, bypassingthe eNodeB (base station). This term is used in contrast with “LTE link”or “LTE (uplink) traffic”, which instead refers to data traffic betweenuser equipment managed by the eNodeB.

The term “transmitting user equipment” used in the claims and in thedescription is to be understood as a mobile device capable oftransmitting and receiving data. The adjective transmitting is onlymeant to clarify a temporary operation. The term is used in contrast to“receiving user equipment”, which refers to a mobile device temporarilyperforming the operation of receiving data.

The term “new data” used in the claims and in the description is to beunderstood as data that arrives/is stored in the transmission bufferwhich was previously not there. This data (data packets) is receivedfrom a higher layer, e.g., IP layer, and placed into the transmissionbuffer. This term is used in contrast to “old data”, referring to datawhich is kept in the transmission buffer as long as the transmissionprotocol makes sure that this data is correctly received at thereceiving side.

The term “arrival” used in the claims and in the description with regardto data and transmission buffers shall be understood as that data, whichis to be transmitted by the user equipment “enters”, or “is put into”,or “is temporarily stored in” the transmission buffer of thecorresponding logical channel for transmission.

In the following, several embodiments of the invention will be explainedin detail. The explanations should not be understood as limiting theinvention, but as a mere example of the invention's embodiments tobetter understand the invention. A skilled person should be aware thatthe general principles of the invention as laid out in the claims can beapplied to different scenarios and in ways that are not explicitlydescribed herein. Correspondingly, the following scenario assumed forexplanatory purposes of the various embodiments shall not limit theinvention as such.

The present invention is mainly directed to the scheduling procedure fordevice-to-device (D2D) communication in LTE systems. A D2D capable userequipment can operate in two modes for the allocation of resources.According to a first operation mode (mode 1), the eNodeB schedules theexact resources which is used by the transmitting user equipment totransmit data to a receiving user equipment over a direct link channel.Specifically, the transmitting user equipment sends a request forallocation of resources to the eNodeB and, based on the request forallocation, the latter schedules the exact resources needed by thetransmitting user equipment to transmit data directly to the receivinguser equipment (scheduled operation mode).

The second operation mode (mode 2), is a collision-based approach.According to this approach, each user equipment has been provided a setof D2D time/frequency resources used for D2D communication, which isalso referred to as resource pool. The transmitting user equipment canautonomously select, from the resource pool, the resources fortransmitting data and control information directly to the receiving userequipment(s) over the direct link communication channel (autonomousoperation mode).

In the scheduled operation mode (mode 1), scheduling information istransmitted to the eNodeB on an uplink data channel. The schedulinginformation may be a Buffer Status Report in a MAC BSR Control Element,which is sent to the eNodeB on a Physical Uplink Shared Control Channel(PUSCH).

A first embodiment of the invention will be explained in connection withFIG. 10, which illustrates the messages exchanged between thetransmitting user equipment (UE1) and the base station (eNB) forscheduling purposes and the data exchange between the transmitting userequipment (UE1) and a receiving user equipment (UE2). The transmittinguser equipment (UE1) requests resources by transmitting buffer statusinformation to the eNodeB over the LTE uplink data channel (PUSCH) andtransmits data to the receiving user equipment over a direct linkcommunication channel. Even though the buffer status information isrelated to D2D data transmission, i.e., data of D2D bearers which issent over the direct link (also referred to as PC5 interface),transmission of the buffer status information is transmitted in an LTEuplink time/frequency resource not in a D2D sub-frame respectivelytime/frequency resource. Specifically, once the eNB receives the BSR, itwill allocate resources from the time/frequency resources which arereserved for D2D data communication, e.g., direct link channel, forallowing the transmitting user equipment (UE1) to transmit data to thereceiving user equipment (UE2). It should be noted that the resourceallocation for D2D data communication respectively the grant whichallocates the D2D transmission resources might be different compared toan LTE uplink grant. For example the D2D resource could be allocated fora longer timeframe, not just for one TTI. In general it is expected thatD2D resource allocations grant is using a new downlink control format(DCI). The DCI may be also scrambled with a new R-NTI, i.e., a D2D RNTIin contrast to the C-RNTI which is used for LTE uplink grants. If thegranted resources are not enough to transmit all the data to thereceiving user equipment (UE2), the eNB will successively grantresources over the direct link channel until the data has beencompletely transmitted by the transmitting user equipment (UE1) to thereceiving user equipment (UE2). In other words, once allocation ofresources has been granted to the transmitting user equipment, thetransmitting user equipment (UE1) and the receiving user equipment (UE2)can communicate with each other without the involvement of, i.e.,bypassing, the network: there is a direct communication channel betweenthe two mobile stations. Data are thus not first sent to the eNodeBusing uplink resources, for instance on PUSCH, and then sent by the backeNodeB via the LTE core network to the user equipment.

As can be seen in the diagram depicted in FIG. 10, the schedulingrequest procedure can be seen as regular LTE traffic, in which thetransmitting user equipment (UE1) contacts the eNodeB in order to askallocation of resources for transmitting data stored in a data buffer ortransmission on the user equipment (not shown), i.e., data stored forthe D2D bearers. Afterwards, once the eNodeB has assigned D2Dtime/frequency resources for transmitting data, the user equipment startdata transmission on the D2D resources, i.e., also referred to as directlink data channel. From this point on time communication between thetransmitting user equipment (UE1) and the receiving user equipment (UE2)will occur without mediation from, i.e., bypassing, the eNodeB.

Alternatively or in addition, a scheduling request may be eithertransmitted via resources of the PUCCH allocated by the eNB, i.e., alsoreferred to as dedicated scheduling request (D-SR), or by using a RACHprocedure. If not indicated differently, in the following we will assumethat such resources of the PUCCH, which are typically allocatedperiodically by the eNB, are available to the UE for transmitting thescheduling request as soon as it is triggered; nevertheless, theinvention is also applicable when using a RACH procedure instead. Adedicated scheduling request is usually one bit long, and correspondingperiodic PUCCH resources allow transmitting the scheduling request butare not sufficient for transmitting further data such as the bufferstatus report or actual data of the transmission buffer. As described inthe technical background section in LTE a scheduling request istriggered for the case that a buffer status report has been triggeredbut there are no PUSCH resources available for the transmission of thebuffer status report. In other words the purpose of the schedulingrequest is to ask eNB for the allocation of PUSCH resources so that UEcould transmit the buffer status report which in turn enables the eNB toallocate adequate resources for the transmission of the uplink data.

According to one embodiment of the invention, the D2D enabledtransmitting UE transmits a scheduling request (SR) either on the PUCCH(D-SR) or performs the RACH procedure (contention based schedulingrequest) when there is a buffer status report triggered for D2D bearers,e.g., when new data arrives for a D2D bearer. This scheduling request istransmitted in a regular LTE uplink time/frequency resource, i.e., noton a time/frequency resource reserved for D2D. Upon receiving thisscheduling request the eNB will allocate PUSCH resources to the D2Dtransmitting UE. The D2D transmitting UE will transmit in turn the D2Drelated buffer status information within this PUSCH resources asdescribed already above. Based on the detailed buffer statusinformation, eNB will allocate D2D time/frequency resources for the D2Ddata communication. For the allocation of the PUSCH resources uponreception of the scheduling request the regular LTE uplink grant/DCIprocedure, i.e., uplink grant is addressed to the C-RNTI, PDCCH/PUSCHtiming relation, is used.

As mentioned above the second uplink grant/resource allocation, i.e.,upon having received the D2D related buffer status information, may usea different resource allocation format/DCI, e.g., addressed to a D2DRNTI.

A more detailed description of the triggering of the scheduling requestwill be given in the following with reference to FIG. 12.

The D2D capable user equipment (not shown) is adapted to send data onboth the LTE uplink data channels and on the direct communication datachannel reserved for D2D communications. To this end some sub-framesrespectively time/frequency resources will be reserved for the LTEuplink traffic, while other sub-frames respectively time/frequencyresources are reserved for D2D transmission, i.e., this could be D2Ddiscovery signaling and/or D2D data communication. Preferably, apredefined time slot will be allocated to each sub-frame in analternating manner following a TDM scheme. As an example, longer timeperiods can be allocated to the signals that require more resources, byreserving more consecutive time slots for the one of the two kinds ofsub-frames mentioned above, while reducing the time period allocated tothe signals requiring less resources.

FIG. 11 describes a composition of a MAC Protocol Data Unit (PDU)according to an implementation of the scheduling method and systemdescribed with reference to FIG. 10. The MAC Protocol Data Unit referredto in the buffer status reporting procedure according to the schedulingmethod described in relation with FIG. 10 incorporates a control elementfor performing D2D related signaling. Preferably, the schedulinginformation for D2D communication may be a D2D dedicated Buffer StatusReport, which may be implemented by a MAC control element for D2Dcommunication. Accordingly, the MAC Protocol Data Unit transmitted onthe PUSCH may include, besides the MAC control elements, such as MACBSR/PHR CEs (indicated in FIG. 11 as MAC CE1 and MAC CE2), used forperforming scheduling in uplink LTE traffic, also one or more D2D MACcontrol element, which will be used for performing scheduling of theresources for transmitting data from the transmitting user equipment tothe receiving user equipment on the direct link channel.

The D2D MAC control element in the MAC PDU may be further associated toan identification number. Said identification number may be, forexample, a reserved logical channel ID, which may be stored in theheader of the MAC PDU, i.e., MAC sub-header. Advantageously, theidentification number may be stored in the R/R/E/LCID sub-headercorresponding to the D2D MAC CE. Accordingly, the eNodeB will be able todistinguish which buffer status report in the MAC PDU has to be used forscheduling procedures of D2D data transmission on the direct linkconnection or for scheduling LTE cellular uplink traffic. This logicalchannel ID is according to one embodiment of the invention one of thereserved logical channel IDs (LCIDs) specified in TS36.321 Table6.2.1-2, incorporated herewith by reference.

The D2D communication method described with reference to FIG. 10 mayfurther include a new enhanced logical channel prioritization (LCP)procedure for LTE uplink transmissions on PUSCH. An LCP procedure iscommonly responsible for allocating data to be transmitted on differentchannels into one MAC PDU. Each D2D-capable user equipment may include amultiplexing unit in the MAC layer (not shown) for multiplexing data ofdifferent logical channels and MAC control elements into said one MACPDU. The MAC control elements will carry for example scheduling relatedinformation used for performing scheduling of both LTE uplink trafficand D2D direct communication.

The LCP procedure defines a relative priority order, according to whichthe user equipment can build the MAC PDU. Advantageously, the LPCprocedure for LTE uplink transmission may define the position or orderof the data parts that compose the MAC PDU. As an explicative exampleonly, the case could be considered, in which 100 bytes are available forthe MAC PDU and the data to be multiplexed into the MAC PDU consists of200 bytes. Based on the LCP procedure, the user equipment will be ableto decide which of the 200 bytes can be transmitted within the MAC PDUand in which order. The remaining 100 bytes of data will then betransmitted in the predefined order in the next MAC PDU, based on thepriorities defined in the LCP procedure. A skilled person will clearlyunderstand that the above example is for illustrative purposes only andthe invention should not be limited to a realization, where 100 bytesare available for the MAC PDU. On the contrary, according to theinvention, more than 100 bytes or less than 100 bytes may be availableto MAC PDU. The number of bytes available for the MAC PDU is a designoption that will be set from case to case depending on the hardwarecharacteristics of the devices, such as the user equipment.

According to an advantageous arrangement, the MAC PDU transmitted on thePUSCH may be organized according to the following priorities indescending order defined in the LCP procedure:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for D2D BSR;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for PHR or Extended PHR;    -   data from any Logical Channel, except data from UL-CCCH;    -   MAC control element for BSR included for padding.

According to the priority order defined by the LCP procedure describedabove, the D2D buffer status report has a higher priority with respectto the buffer status report used for performing a scheduling procedurefor LTE cellular uplink traffic.

Clearly, the above order is merely an example for explicative purposes.According to a further advantageous arrangement, more importance couldbe given to the LTE traffic by assigning a higher priority to the bufferstatus report corresponding to LTE uplink traffic. Accordingly, the LCPprocedure for D2D-capable UE may define the following priorities indescending order:

-   -   MAC control element for C-RNTI or data from UL-CCCH;    -   MAC control element for BSR, with exception of BSR included for        padding;    -   MAC control element for D2D BSR;    -   MAC control element for PHR or Extended PHR;    -   data from any Logical Channel, except data from UL-CCCH;    -   MAC control element for BSR included for padding.

Again, the examples of LCP procedures reported above are only two ofseveral possible options for the definition of relative priorities anddo not have to be considered as limiting the invention. Other priorityorders can be clearly defined according to the network configuration andcommunication specifications.

A common Buffer Status Reports in LTE systems can be 1 or 4 bytes long(respectively short and long BSR). In addition a truncated BSR of 2bytes can be also used as described in the introductory portion, section“Buffer Status reporting/Scheduling Request procedure for uplinkscheduling”.

In a D2D communication scenario, communication set up is notmanaged/configured by the eNodeB but rather by a separate entity, e.g.,such as a D2D server in the core network or respectively a D2DManagement entity in the UE. The D2D Management entity which could bealso referred to as ProSe Management Entity (PME) resides in the UE andis provisioned with configuration parameters, e.g., protocol/bearerconfiguration, used during D2D communication. The provisioning isperformed by pre-configuration or, in case of network coverage, bysignaling between the PME and the D2D Function/server in the corenetwork. To support D2D communication over “D2D Bearer”, the PME thenconfigures Layer 2 and the physical layer based on the in beforehandprovisioned configuration parameters. Since the eNodeB is not aware ofthe detailed configuration parameters for data transfer over the D2Ddirect link connection, such as which D2D bearers the user equipment usefor data transfer, no quality of service (QoS) control from the networkpoint of view as ensured for LTE traffic is provisioned for D2D datacommunication. Since the detailed D2D bearer configurations maybe notknown to eNB the D2D Buffer Status Report may advantageously includeonly the amount of data which is in the buffer for all D2D bearers. Thiswould be in contrast to an BSR for LTE traffic/bearers which isorganized on logical channel group level.

In addition to information on the amount of data of D2D bearers storedin the transmission buffer, the D2D BRS MAC CE may furtheradvantageously include some further information which allows for moreefficiently scheduling of D2D data communication by eNB. As an examplethe D2D buffer status report may according to another embodiment of theinvention include an indication of the D2D traffic or bearer type forwhich D2D time/frequency resources should be allocated by eNB.Advantageously, the D2D BSR MAC CE may include one or more type-flagsindicating the traffic or bearer type. As an example, a type-flag mayinclude information on whether the data to be transmitted on the D2Ddirect link channel is speech data, or another non-conversional type ofdata, such as video data.

Based on the type flag, which carries information on the traffic bearertype, the eNodeB can schedule resources more efficiently. As an example,from the type-flag the eNodeB may derive that the transmitted data arespeech data, such as VOIP data. Accordingly the eNodeB may allocate theresources' priority, in the usual manner as done for speech datatransmission on LTE uplink data channel. Specifically, the eNodeB canallocate resources for transmitting a certain amount of bitsperiodically. As an example, for a speech signal, which is a periodicsignal, the eNodeB may allocate resources for transmitting over the D2Ddirect link data channel resources every 20 ms.

In contrast thereto, if the type-flag indicates that the data to betransferred over the D2D direct link data channel is a non-conversationservice, such as video data, the eNodeB may allocate, based on thetype-flag information in the BSR, the resources not periodically butrather as a one-time allocation.

In conclusion, for LTE communication, the traffic is controlled by thenetwork, and, therefore, the eNodeB has information about, for instance,which QoS the different bearers need to support. However, the eNodeBcannot retrieve this information for D2D data traffic, since the latteroccurs without the mediation of the network. Consequently, together withthe buffer status report the user equipment has to provide thisinformation to the eNodeB for D2D communications. To this end thetype-flag information in the BSR may advantageously provide the eNodeBwith information about the bearers and the data traffic on the D2Ddirect link channel, which are otherwise not directly obtainable by theeNodeB. This information could be then also used by the eNB in order toprioritize D2D resource allocation among several D2D transmitting UEs.As an example when eNB receives multiple scheduling requestsrespectively D2D related buffer status information the eNB needs toprioritize the resource allocations. This could be for example doneaccording to some further alternative embodiment based on some priorityinfo included in the D2D buffer status MAC CE. The priority info may befor example retrieved from the PME which configures Layer 2 and thephysical layer based on the in beforehand provisioned configurationparameters as outlined above. As an example for each D2D bearer the PMEcould associate a priority value similar to the logical channel priorityfor LTE bearers. When a D2D transmitting UE intends to transmit D2Ddata, it may for example include the priority value of the highestpriority D2D bearer for which the UE requests transmission resources.

A user equipment is provided with transmission buffer memory for thedata of each logical channel, used for temporarily storing uplink datauntil it is successfully transmitted over the radio link to the eNodeB.Furthermore, the UE has no uplink resources available to transmit thedata or a buffer status report to the base station, making it thusnecessary to transmit a scheduling request to the eNB, which processshall be improved by the first embodiment of the invention.

In the configuration explained in connection with FIG. 10, thetransmitting user equipment sends a D2D related buffer status report tothe eNB when data of D2D bearers to be transmitted over the D2D directlink data channel is temporarily stored in the transmission buffer ofthe transmitting user equipment.

In addition, the triggering of the D2D buffer status report may beimmediately followed by the triggering of a scheduling request, providedno uplink shared channel resources (UL-SCH) are available to transmitthe triggered buffer status report.

As explained before, scheduling requests may be either transmitted viaresources of the PUCCH allocated by the eNodeB or by using a RACHprocedure. If not indicated differently, in the following we will assumethat such resources of the PUCCH, which are typically allocatedperiodically by the eNodeB, are available to the UE for transmitting thescheduling request as soon as it is triggered; nevertheless, theinvention is also applicable when using a RACH procedure instead. Ascheduling request is usually one bit long, and corresponding periodicPUCCH resources allow transmitting the scheduling request but are notsufficient for transmitting further data such as the buffer statusreport or actual data of the transmission buffer. Furthermore based onthe scheduling request the eNB is not aware of whether the UE requeststransmission resources for a direct link transmission (D2D datatransmission) or for a LTE uplink transmission. Only based on the bufferstatus report as outlined above the eNB can distinguish a request forD2D transmission and a LTE uplink transmission.

FIG. 12, illustrates the transmission buffer at the user equipment andthe messages exchanged with the base station to request resources fortransmitting data on the D2D direct link data channel. In addition FIG.12 describes the transmission of the buffer status report on the uplinkdata channel, and the scheduling request to the eNodeB, and data to thereceiving user equipment over the direct link data channel. FIG. 13illustrates the process at the transmitting user equipment forperforming message and data exchange depicted in FIG. 12.

According to the configuration illustrated in FIG. 12, the triggering ofthe buffer status report/scheduling request for D2D data communicationmight rely on different conditions compared to the standard triggering.As one example the D2D buffer status report/scheduling request could betriggered only when a certain amount of data has been piled up in thecorresponding buffers. Postponing the buffer status report/schedulingrequest allows that more data arrives in the transmission buffer, andthus uplink transmissions transport more data in less time.Correspondingly, the triggering of the buffer status report/schedulingrequest is performed when sufficient data is in the transmission buffer,and not immediately when new data arrives in the empty transmissionbuffer. It is more power efficient to transmit larger Transport Blocksizes, rather than transmitting smaller Transport Block sizes.

The configuration of FIG. 12 may be implemented in the followingexemplary way. The triggering of a buffer status report in the userequipment depends on two conditions, which shall be both fulfilled. Bothtrigger conditions in the context of an LTE implementation relate to thetransmission of a buffer status report, which, however, directly leadsto a transmission of a scheduling request, since it is assumed that noresources are available for the user equipment to transmit the triggeredbuffer status report; thus, it can be also said that the triggerconditions are defined for the transmission of the scheduling requesttoo.

The first trigger condition requires new data to become available in thetransmission buffer, which means that data from higher layers shall betransmitted over the direct link data channel to the receiving userequipment (UE2) and is thus entered into the transmission buffer of thetransmitting user equipment (UE1). It should be noted that the firsttrigger condition is fulfilled independently from whether thetransmission buffer is empty or not and independently from the priorityof the new data, as long as new data becomes available in thetransmission buffer.

This behavior is depicted in FIG. 13, where the transmitting userequipment (UE1) checks whether new data arrives in its transmissionbuffer.

The second trigger condition is basically responsible for postponing thetriggering of the buffer status/scheduling request; it requires thatthere is enough data in the transmission buffer of UE1. Correspondingly,the data in the transmission buffer shall in general surpass apredetermined threshold.

For the second trigger condition the user equipment checks for examplewhether the amount of data in the transmission buffer changed of apredetermined value Δd compared to the amount of data stored in thetransmission buffer at the time the previous Buffer Status Report wastriggered/sent to the eNodeB.

In FIG. 13 it is assumed that the transmitting user equipment checks thesecond trigger condition requiring the amount of data to change of apredetermined value. Though it appears logical to check the first andsecond trigger condition in the order as illustrated in FIG. 13, i.e.,first the first trigger condition and then the second trigger condition,this is not necessary. The user equipment may also first check thesecond trigger condition and then the first trigger condition.

It should be also noted that if the second trigger condition (requiringthe data amount to change of a predefined value) is fulfilled, thisautomatically requires that the first trigger condition is fulfilled. Inother words, the amount of data in the transmission buffer can only thensuddenly change of a predetermined data amount, if new data arrives inthe transmission buffer, which corresponds to the requirement of thefirst trigger condition. Thus, in one alternative, the first triggercondition does not necessarily need to be checked; it suffices to checkonly the second trigger condition such that the BSR/SR is triggered whenthe amount of data in the transmission buffer exceeds a certainthreshold.

In the example above the transmission of BSR is triggered by the changeof the data amount in the transmission buffer of a predetermined amountwith respect to the amount of data in the transmission buffer at thetime of the previous BSR triggering/transmission. However, othertriggering schemes may be used instead of the one described above.Alternatively, the transmission of BSR may be triggered, if the amountof data in the transmission buffer of the transmitting user equipmentexceeds a predefined threshold.

A further aspect of the invention relates to the rules for theinclusion/multiplexing of a D2D BSR into a MAC PDU transmitted on PUSCH.According to the current LTE specifications (Rel-8/9/10/11) the UE isonly allowed to include at most one BSR MAC CE in a MAC PDU. However,according to one embodiment of the invention a D2D-capable UE is allowedto multiplex one D2D BSR MAC CE and one LTE BSR MAC CE in a MAC PDUwhich is transmitted on PUSCH to the eNB. This ensures that the regularLTE uplink scheduling procedure is not delayed or impacted due to theD2D scheduling procedure.

In an alternative implementation of the system and method describedabove, the restriction of including at most one BSR MAC in a MAC PDU maybe kept. This alternative implementation would use a structure of theMAC PDU which is similar to that known for standard LTE systems, withthe difference that the MAC PDU may include a D2D BSR MAC CE instead ofa LTE BRS MAC CE. Such a configuration would result in a delay in thetransmission of either the LTE BSR MAC CE or the D2D BSR MAC CE.Further, since only one of the LTE BSR MAC CE and the D2D BSR MAC CEwill be included in the MAC PDU, new prioritization rules would need tobe defined.

Yet another aspect of the invention is related to the cancellationprocedure of a buffer status report. According to the regular buffersstatus reporting procedure specified in TS36.321 version 11.2.0, section5.4.5, which is herewith incorporated by reference, all triggered BSRsmay be cancelled when a BSR is included in a MAC PDU for transmission.According to a further embodiment of the invention a D2D capable UE maynot cancel a regular “LTE buffer status report” when a D2D buffer statusreport is included in a MAC PDU for transmissions. This solution ensuresthat the regular LTE uplink scheduling/buffer status reporting procedureis not impacted by the introduction of a D2D buffer status report.

Similarly and according to yet another aspect of the invention theScheduling Request (SR) prohibit timer may not be started when thescheduling request was triggered only due to the fact that a D2D Bufferstatus report was triggered. A D2D capable UE may according to a furtherembodiment of the invention not start the SR prohibit timer when SR hasbeen transmitted on PUCCH for the case that the SR was only sent inorder to request transmission resources for a D2D communication.Similarly to the embodiments outline just above a D2D BSR may not delaythe LTE data transmission, i.e., in particular high priority LTE datalike RRC signaling.

Another aspect of the invention relates to the selection of the resourceallocation mode for D2D data communication. As described above there aretwo modes in which the UE can operate for the resource selection for D2Ddata communication, i.e., scheduled operation mode (model) andautonomous operation mode (mode2). The general principle should be,according to one embodiment, that the eNB controls the resourceallocation mode a D2D capable UE operates in. According to oneadvantageous implementation a D2D capable UE, which has to transmit dataof a D2D bearer, may always first operate in mode 1, i.e., establishingan RRC connection to the eNB (for the case of an RRC_IDLE UE) andsending buffer status report/scheduling request to the eNB as outlinedin the previous embodiments.

If UE doesn't receive any resource allocation for D2D transmission fromthe eNB, e.g., within a predefined time window, or alternatively anexplicit signaling indication from eNB which indicates the UE toautonomously select D2D time/frequency resource from a resource pool forD2D data transmission, the UE will fall back to mode 2 operation.Alternatively the eNB could signal, e.g., by means of system informationbroadcasting (SIB), that scheduled mode operation is not supportedwithin this cell. A flag may be for example broadcasted which indicatesthe availability of mode 1 within this cell. Based on this flag a D2Dcapable transmitting UE will either first try the mode 1 type ofoperation (when the flag indicates that mode 1 is operated in the cell)or immediately use mode 2 for the resource allocation for D2Dtransmissions. Yet another solution may be that some special accessclasses could be introduced which are reserved for D2D purposes andbased on those access classes the eNB could control which D2D UEs areallowed to request resources for D2D data transmission directly from theeNB, i.e., use mode 1 type of operation. Basically each D2D UE would beassigned an access class and some signaling from the eNB will indicatewhich classes are allowed to use mode 1 for resource allocation.

Still a further aspect of the invention relates to the LCP procedure inUE capable of supporting device-to-device communication. The userequipment may have both LTE channels or bearers for transmitting dataover the uplink data channel and D2D bearers. In such a scenario, dataof the D2D bearers may be only transmitted in D2D sub-frames or, inother words on resources configured for D2D transmission over the directlink data channel. Similarly, data of the LTE bearers may be onlytransmitted in LTE-dedicated sub-frames respectively time/frequencyresources. Further, a logical channel prioritization procedure may beimplemented, which takes into account the UE capability of transmittingover the LTE uplink channel and over the direct link channel.

In an advantageous implementation, a common LCP procedure may bedeveloped for both the LTE and D2D bearers. Accordingly, in LTEsub-frames data of D2D bearers will not be considered for the LCPprocedure. In other words, D2D bearers may be considered suspended forthe LCP procedure in LTE sub-frames respectively time/frequencyresources. Similarly, LTE bearers may be suspended for the LCP operationin D2D sub-frames. Having a common LCP procedure for D2D and for LTEcommunication, allows reducing the complexity of the management of D2Dand LTE bearers.

Alternatively, there may be two separate LCP procedures: one for D2Ddata transfer over the direct link channel, and one for LTE datatraffic. Accordingly, a dedicated LCP procedure for D2D bearers may beinvoked for D2D sub-frames whereas the LCP defined for LTE is invoked inthose sub-frames which are reserved for LTE only transmissions. Sincethere is no QoS support for D2D bearers, and therefore no PrioritizedBit Rate (PBR) needs to be set, the D2D LCP procedure in this scheme maynot need the use of the token bucket model. The scheme in which twoseparate LCP procedures for D2D and LTE are given may have theadvantage, that the D2D LCP procedure can have an easier configuration.

Still a further aspect of the invention relates to the uplinktransmission timing of discovery signals. In general the transmissiontiming in D2D data transmission will be different than the transmissiontiming in LTE uplink data transmission. This is due to the fact that inLTE, the timing of a user equipment is always controlled by the network,i.e., by the eNodeB. Specifically, the network controls that all theuplink signals from all the user equipment under the control of theeNodeB are received at the same time, in order to avoid interference. Ina system capable of device-to-device communication the transmitting userequipment that transmits data to a receiving user equipment over thedirect link data channel has to negotiate some timing with the receivinguser equipment (or group of receiving user equipment). The timingnegotiated by the transmitting and the receiving user equipment may bydifferent than the network-controlled timing for LTE uplink datatraffic. According to a first solution the RRC_Connected D2Dtransmitting user equipment transmits a discovery signal based on thedownlink reference timing also for D2D communication. In LTE systems,the uplink timing is defined as the downlink reference timing plus anoffset as correction to the downlink timing. The offset in called timingalignment (TA) factor and its value is controlled by the eNodeB.According to the first solution, the correction value for the uplinkwill be, therefore, zero (T2=0) for D2D in FDD. In TDD RRC_connected andRRC_idle D2D transmitting user equipment may transmit discovery signalbased an offset of 624 Ts. As a result, the downlink timing will beT2=624 Ts.

Since two different timings for LTE and D2D discovery/communication aregiven, the user equipment in RRC_Connected state may have two separate,independent timing alignment functionalities residing in the MAC layer,which include timing alignment values and or Timing alignment timers:i.e., one for D2D and one for LTE.

Advantageously, uplink timing functionality for D2D may be activatedonly for D2D sub-frames. In other words, there will be an uplink timingjump between an LTE uplink sub-frame and D2D transmission. In addition,NTA_Ref_D2D for D2D discovery may be set to zero

According to a further advantageous aspect, which may be used togetheror in alternative to the previously described aspects, an autonomousuplink timing adjustment (tracking DL reference timing) may be appliedto D2D transmission during D2D sub-frames.

Finally, for D2D communication the user equipment will not receiveTiming Advance (TA) commands from eNodeB. Consequently, according to afurther advantageous aspect, which may be used together or inalternative to the previously described aspects, a Timing Advance timerfor D2D may be given. As an example, a TA timer may be set to infinityfor D2D communications and started before the first D2D discovery ortransmission occurs.

Another aspect of the invention is related to the discovery procedurefor Device-to-Device communication respectively proximity services. Inout of coverage, there is no network available and therefore a dedicatedor common/resource allocation from the network side is not possible fortransmitting/receiving discovery resources. A further embodiment of thepresent invention addresses the above problem. Accordingly, a D2Dcapable UE which is not in the coverage of a network, i.e., alsoreferred to as out-of-coverage, may transmit a fixed sequence at a fixedfrequency that is repeated periodically with a fixed period. Theprocedure described above may be implemented by transmitting D2D PrimarySynchronization Signals with no device identity or with ProSe UEIdentities, on a fixed frequency irrespective of its actual frequency ofoperation. Such an implementation allows to perform detection by otherD2D UEs in a very simple manner.

For D2D capable UEs which are in the coverage of a network, i.e.,referred to as in-coverage UEs, the discovery procedure can bedistinguished between Idle mode UEs and connected mode UEs, i.e., UEshaving established a RRC connection to the network. The two modes willbe described in the following.

Idle UE

According to the first in-coverage discovery procedure, both Type1 andType2 resources in the current cell for D2D discovery messages reception(Rx Pool) may be broadcasted in System Information. In addition, thecurrent cell may also broadcast the Tx Pool from a neighboring cell (andpossibly also the out of coverage Tx Pool) which could be on a same ordifferent frequency. The discovery message reception is thus given by:

Rx Pool=Tx Pool of current cell+Tx Pool of neighbor cell(s)+Out ofCoverage Tx Pool

Alternatively, in some deployments, the Tx Pool of neighbor cell(s)and/or Out Of Coverage TX Pool may not be broadcasted by the currentcell, since it might be an operator's choice to save broadcasting and/orsince the neighbor cell may belong to a different PLMN, etc. In such acase, the current cell may at least indicate that Rx Pool broadcasted inthe current cell may not contain all Tx Pools of interest from outsidethis cell. In simplest form this could be 1 bit indication (indicated asnote1 in the below diagram) in the D2D System information block.

Further, a receiving UE needs to determine if there would be other D2Ddevices outside this cell, whose discovery message(s) may also be ofinterest to said receiving UE. Accordingly, said information may betransmitted by a higher layer, e.g., a NAS application (based on, e.g.,Prose server). Upon such a determination, that some D2Ddevices/discovery of interest are unavailable in this cell, the UE willbe able to find out the possible neighbor cell(s) where such D2Ddevices/discovery of interest may be present.

The method for deceiving D2D discovery signals as described above isshown in FIG. 14.

According to an implementation of the D2D capable communication system,the neighbor cells that support D2D discovery (i.e., have allocatedcertain resources for Type 1 and/or Type 2 resources) may lie on adifferent frequency. In such a case an indication of both PCI andfrequency of neighbor cells may advantageously done in the systeminformation broadcast of the current cell.

FIG. 15 schematically illustrates a situation in which a D2D capable UEperforms discovery in neighboring cells. The discovery transmissions arelimited by the maximum Tx power of the transmitting UE and thereforediscovery transmissions in far-away cells will not be receivable to thisD2D device.

Therefore, according to a further implementation, a D2D device waitingto receive discovery messages from neighboring cell(s) may not need tosearch/acquire all possible neighbor cells but only that are close toit. As an example, as shown in the below diagram, the D2D device doesnot try to detect/acquire D2D resources of neighbor cell 2 since anypossible transmission from a D2D device in neighbor cell 2 is too faraway/unreachable. Advantageously, a UE may try to detect/acquire D2Dresources of neighbor cell-x only if certain conditions are fulfilled.Advantageously, the UE may decide whether to detect or acquire D2Dresources of a neighboring cell x (cell-x) if:

Current_Cell_Quality−Cell_x_Quality<Threshold1; or,

Cell_x_Quality>=Current_Cell_Quality

Connected Mode

The information about Rx Pool may be signaled to a UE in connected modeby dedicated signaling (e.g., RRC information). The Rx Pool may includeinformation about Tx Pool of neighbor cell(s) and/or Out Of Coverage TXPool. Alternatively, the UE may acquire the information as described inrelation with the Idle Mode discussed above.

In addition, a connected mode UE may also require Gap patterns toacquire (a) detection of inter frequency neighbor cell(s), and their D2DSI; and (b) the discovery message(s) on inter-frequency resources.

Accordingly, such a UE may ask for Gap pattern from the serving eNBpossibly including the information about the possible gaps (gap length,repetition length, offset etc.). Alternatively, such a UE may useautonomous gaps.

As the previous embodiment was mainly focusing on the receivingoperation of D2D discovery in the following the transmitting operationfor D2D discovery is described according to one exemplary embodiment ofthe invention.

A D2D capable UE may need to decide between which type of resource itshould use to transmit D2D discovery signals/messages. Based on thisdecision it may need to request resources accordingly at the eNB (e.g.,for Type 2B resources) and it may therefore need to establish an RRCconnection for this purpose (if the UE was in Idle Mode).

According to an advantageous implementation the decision on the type ofresources that should be used to transmit D2D discovery signals ormessages may be based on the following criteria:

1) Type of Discovery, i.e., based on Application triggering Discoverytransmission

-   -   Mapping between Discover resource type and Application could be        specified, pre-configured, indicated by the (Pro-se) Discovery        Server etc.;        2) Last successful Discovery Transmission (e.g., For the same        Discover application);

3) Idle Mode Mobility State.

Advantageously in one implementation, Slow or stationary UEs may alwaysask for a particular resource type (e.g., Type 2B); mobile UEs (e.g.,Medium mobility) will use, e.g., Type 1. The types of request mentionedabove will be explained in the following sections.

Request for Type 2B Resources

If the UE decides to use Type 2B resources, it shall request eNB to havethese Type 2B resources granted. This can be accomplished by thefollowing procedures:

-   -   Using Special RACH resources (e.g., Preamble, RACH transmission        resources);    -   A new cause value(s) in msg3 (RRC Connection Request)—to ask for        D2D Type 2B Tx resources        -   Since the UE does not intend to establish an LTE bearer            (e.g., one terminating in the LTE CN) a Light RRC protocol            can be used for this purpose, e.g., no security context may            need to be established, no measurements            configuration/reporting etc.;    -   NAS signaling        -   UE NAS informs MME, MME verifies and indicates/requests eNb            to use Type 2B; eNB grants Type 2B resources to this UE (in            RRC Reconfiguration). Application to Resource mapping is            fixed and therefore Pro-se server/application/CN decide the            resource type to be used, e.g., During Authentication of D2D            services.

Additionally, the UE may indicate the estimated length of Type 2Bresource usage while requesting for such a resource. If the request isnot honored (e.g., UE receives a 2B resource reject message/RRCconnection release, or no response within certain time), the UE startsusing Type 1.

Mobility (Handover, Re-Establishment)

The mobility will not ensure that the D2D resources allocated previouslyare still available for use. Then there are following treatment to theallocated D2D resources during mobility:

-   -   Kept as it is        -   Negotiated on X2; e.g., Neighbors reserve the same physical            resources for D2D Discovery transmission    -   Reconfigured by target in HO Command/Reestablishment        msg.+Reconfig. Msg.;    -   De-configured/released as a result of receiving HO Command;        -   UE asks for the same after Handover in the target cell            (target eNB may allocate same-as-in-previous cell or new            resources)

Releasing Discovery Resource Type 2B

According to an advantageous implementation, the dedicated resources(type 2B) may be released by the UE when the same is no longer required(i.e., the UE would not transmit D2D discovery). Alternatively, the eNBmay request the resources back (e.g., to avoid congestion in LTEcellular communication). Such a release may be done as described in thefollowing:

-   -   Implicit Release        -   Upon a timer (configured/specified) expiry            -   If the UE wish to retain it (Type 2B resources) further,                it needs to send a “keep-alive” signaling to eNB.        -   Upon mobility (handover, reestablishment): the UE simply            relinquishes the Type 2B resource used in the source cell.        -   Upon RRC Connection Release (already decided in RAN2#85):            the UE simply relinquishes the Type 2B resource used in the            source cell.    -   Explicit Release        -   New Signaling (RRC, MAC CE etc.)            -   from UE (initiating release 2B) when it no more needs                it;            -   from network (initiating release 2B) in case of                congestion in LTE (overlay) network.

Upon network initiating the release of Type 2B resources, UE may startusing Type 1 resources, if it still needs to transmit discoverymessages/signals.

D2D Related System Information Broadcast (SIB)

A D2D SIB is the broadcast of information pertaining to D2D discovery inthe underlay network. This information may not be used/useful to UEsonly interested in the overlay (LTE) network. The network may broadcastinformation related to D2D (called D2D SIB(s)) in separate SystemInformation Blocks (SIB). Same or different SIBs may indicate the D2Dresources for Receiving Inter cell Discovery messages.

Receiving Resources in Current Cell=Transmitting Resources in CurrentCell+Transmitting Resources from Neighbor Cell

Change of D2D SIBs

A new paging message could be used (New D2D P-RNTI) which carriesinformation about D2D SIB modification. Alternatively, Timer based (notchange more frequently than ‘x’ ms.) mechanism can be used such that theinterested D2D device must re-acquire the D2D SIB (only) at timerexpiry. As another alternative, a D2D SIB modification may impact thevalue tag in SIB1 as today or may even have its own value tag.

Hardware and Software Implementation of the Invention

Another aspect of the invention relates to the implementation of theabove described various embodiments and aspects using hardware andsoftware. In this connection the invention provides a user equipment(mobile terminal) and a eNodeB (base station). The user equipment isadapted to perform the methods described herein. Furthermore, the eNodeBcomprises means that enable the eNodeB to evaluate the IPMI set qualityof respective user equipment from the IPMI set quality informationreceived from the user equipment and to consider the IPMI set quality ofthe different user equipment in the scheduling of the different userequipment by its scheduler.

It is further recognized that the various embodiments of the inventionmay be implemented or performed using computing devices (processors). Acomputing device or processor may for example be general purposeprocessors, digital signal processors (DSP), application specificintegrated circuits (ASIC), field programmable gate arrays (FPGA) orother programmable logic devices, etc. The various embodiments of theinvention may also be performed or embodied by a combination of thesedevices.

Further, the various embodiments of the invention may also beimplemented by means of software modules, which are executed by aprocessor or directly in hardware. Also a combination of softwaremodules and a hardware implementation may be possible. The softwaremodules may be stored on any kind of computer readable storage media,for example RAM, EPROM, EEPROM, flash memory, registers, hard disks,CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments of the invention may individually or in arbitrarycombination be subject matter to another invention.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A base station comprising: a receiver, which, in operation, receivesfrom a communication apparatus a direct link Buffer Status Report (BSR)for a device to device (D2D) communication, wherein the direct link BSRis a message that informs the base station of an amount of D2D data tobe transmitted from the communication apparatus to a destination userequipment; and a transmitter, which, in operation, transmits to thecommunication apparatus a D2D grant that schedules D2D resources for theD2D data, wherein an uplink BSR has a higher priority in resourcescheduling than the direct link BSR, the uplink BSR being a message thatinforms the base station of an amount of uplink data to be transmittedfrom the communication apparatus to the base station.
 2. The basestation according to claim 1, wherein the direct link BSR is transmittedin a direct link BSR MAC control element with an index identifying atype of the D2D data and/or with a MAC header that includes a logicalchannel ID.
 3. The base station according to claim 1, wherein the D2Dresources are a set of subframes for the D2D communication.
 4. Thecommunication apparatus according to claim 1, wherein the direct linkBSR includes the amount of D2D data and one or more additional pieces ofinformation relating to the D2D communication.
 5. The base stationaccording to claim 1, wherein the receiver, in operation, receives fromthe communication apparatus a Scheduling Request (SR) requestingresources for the direct link BSR.
 6. The base station according toclaim 1, wherein the direct link BSR is a first type of direct link BSRor a second type of direct link BSR that is shorter in data length thanthe first type of direct link BSR.
 7. The base station according toclaim 1, wherein at most one (1) direct link BSR MAC control elementincluding the direct link BSR and one (1) BSR MAC control elementincluding the uplink BSR are transmitted in a MAC Protocol Data Unit(PDU).
 8. The base station according to claim 1, wherein the direct linkBSR is transmitted on Uplink Shared Channel (UL-SCH) resources, whichare different from the D2D resources.
 9. The base station according toclaim 1, wherein the uplink BSR is transmitted in a MAC Protocol DataUnit (PDU) even when both of the uplink BSR and the direct link BSR aretriggered.
 10. The base station according to claim 1, wherein one uplinkBSR and one direct link BSR are transmitted in a MAC Protocol Data Unit(PDU) even when both of the uplink BSR and the direct link BSR aretriggered.
 11. A communication method comprising: receiving from acommunication apparatus a direct link BSR, wherein the direct linkBuffer Status Report (BSR) is a message that informs the base station ofan amount of D2D data to be transmitted from the communication apparatusto a destination user equipment; and transmitting to the communicationapparatus a D2D grant that schedules D2D resources for the D2D data;wherein an uplink BSR has a higher priority in resource scheduling thanthe direct link BSR, the uplink BSR being a message that informs thebase station of an amount of uplink data to be transmitted from thecommunication apparatus to the base station.
 12. The communicationmethod according to claim 11, wherein the direct link BSR is transmittedin a direct link BSR MAC control element with an index identifying atype of the D2D data and/or with a MAC header that includes a logicalchannel ID.
 13. The communication method according to claim 11, whereinthe D2D resources are a set of subframes for the D2D communication. 14.The communication method according to claim 11, wherein the direct linkBSR includes the amount of D2D data and one or more additional pieces ofinformation relating to the D2D communication.
 15. The communicationmethod according to claim 11, comprising receiving from thecommunication apparatus a Scheduling Request (SR) requesting resourcesfor the direct link BSR.
 16. The communication method according to claim11, wherein the direct link BSR is a first type of direct link BSR or asecond type of direct link BSR that is shorter in data length than thefirst type of direct link BSR.
 17. The communication method according toclaim 11, wherein at most one (1) direct link BSR MAC control elementincluding the direct link BSR and one (1) BSR MAC control elementincluding an uplink BSR are transmitted in a MAC Protocol Data Unit(PDU).
 18. The communication method according to claim 11, wherein thedirect link BSR is transmitted on Uplink Shared Channel (UL-SCH)resources, which are different from the D2D resources.
 19. Thecommunication method according to claim 11, wherein the uplink BSR istransmitted in a MAC Protocol Data Unit (PDU) even when both of theuplink BSR and the direct link BSR are triggered.
 20. The communicationmethod according to claim 11, wherein one uplink BSR and one direct linkBSR are transmitted in a MAC Protocol Data Unit (PDU) even when both ofthe uplink BSR and the direct link BSR are triggered.